Norpiperidine imidazoazepines as a new class of potent, selective, and nonsedative H1 antihistamines

Article abstract of DOI:10.1021/jm049495j

Clinical doses of available H₁ antihistamines are limited mainly by sedative side effects. However, higher doses are often required to obtain optimal therapeutic activity, especially in dermatology. We report the synthesis of three norpiperidin

Full text of DOI:10.1021/jm049495j

2154
J. Med. Chem. 2005, 48, 2154-2166
Norpiperidine Imidazoazepines as a New Class of Potent, Selective, and
Nonsedative H1 Antihistamines
Frans Janssens,*,† Jos Leenaerts,† Gaston Diels,† Benoˆıt De Boeck,† Anton Megens,‡ Xavier Langlois,§
Koen van Rossem,| Johan Beetens,| and Marcel Borgers|
Medicinal Chemistry Department, General in Vivo Pharmacology Department, CNS-Psychiatry 1 Department,
Johnson & Johnson Pharmaceutical Research & Development, a division of Janssen Pharmaceutica NV,
Turnhoutseweg 30, B-2340 Beerse, Belgium, and Barrier Therapeutics, Cipalstraat 3, B-2440 Geel, Belgium
Received June 25, 2004
Clinical doses of available H1 antihistamines are limited mainly by sedative side effects.
However, higher doses are often required to obtain optimal therapeutic activity, especially in
dermatology. We report the synthesis of three norpiperidine imidazoazepines representative
of a new class of selective and nonsedating H1 antihistamines. The compounds were at least
as potent as cetirizine and loratadine as measured by H1 receptor binding affinity, by protection
against compound 48/80- and histamine-induced lethality in rats and guinea pigs, respectively,
and by skin reaction tests in rats, guinea pigs, and dogs. The compounds, in particular 3a,
were less prone than the reference compounds to penetrate the brain and to occupy central H1
receptors, suggesting absence of sedative side effects. In vitro and in vivo cardiovascular safety
tests showed that 3a had no intrinsic potential to prolong ventricular repolarization or induce
cardiac arrhythmias. Compound 3a has been selected for further clinical development, mainly
for application in dermatology.
Introduction
free from sedative effects at the recommended clinical
dose. However, when the dose is increased, there is
increasing evidence of sedative activity. This sedative
activity will compromise patients who, due to clinical
need and their particular symptoms, require more than
the recommended dose of medication, a condition com-
monly encountered in dermatological disorders.9 On top
of the already existing requirements to obtain cardiosafe
antihistamines, truly nonsedating properties, even at
higher than recommended clinical doses for the treat-
ment of rhinitis, represent now an important criterion
to differentiate the members of a new class of third-
generation H1 receptor antagonists from the current
commercialized “nonsedating” antihistamines.
Herein, we report the synthesis of three nonsedating
H1-antihistamine development candidates, 1, 2a, and
3a (Figure 1), of the norpiperidine imidazoazepine class.
To compare the title compounds with other antihista-
mines, such as loratadine (Claritin, 4) and cetirizine
(Zyrtec, 5), we have evaluated their physicochemical
properties, their in vitro and in vivo pharmacology, and
their potential to cross the blood-brain barrier. As
antihistamines are regarded as a pharmacological class
of compounds with a potential for cardiac side effects,
we also evaluated the in vitro and in vivo cardiovascular
safety of the title compounds. All these results taken
together have led us to select compound 3a (Hivenyl)
for clinical evaluation.
It is widely accepted that the antihistamines have
found their greatest therapeutic potential in the treat-
ment and management of various allergic disorders,
including seasonal and perennial rhinitis, as well as in
urticaria and other dermatological disorders. Antihis-
tamines are among the most commonly prescribed
drugs, and numerous reviews are available.1 Due to
their ability to cross the blood-brain barrier, sedation
is the most common side effect observed with the first
generation of antihistamines. Sedation may severely
impair daytime activities, including school performance,
driving ability, and many tasks that require concentra-
tion and a high degree of alertness.1d Furthermore,
daytime sedation also reduces patient compliance and
consequently the efficacy and usefulness of sedating
antihistamines.1d Although there is no doubt that
significant improvements have been observed with the
less- or nonsedating H1 antihistamines of the second
generation, such as astemizole,2 terfenadine,3 cetiriz-
ine,4 and loratadine,5 it is also clear today that many
members of this class are not free of all side effects. For
example, terfenadine and astemizole have been associ-
ated with prolongation of the QT interval and fatal
cardiac arrhythmias at high concentrations, resulting
in the withdrawal of the compounds from the major
markets.6 On the other hand, antihistamines such as
cetirizine, loratadine, and desloratadine7 penetrate the
central nervous system (CNS) and display dose-related
impairment of CNS function.1d,8 The drugs are relatively
Chemistry
As a general approach to the family of compounds
derived from 1, 2a, and 3a, we have developed an acid-
catalyzed ring-closing pathway to the imidazoazepine
ring system.10 Therefore, the syntheses of the three
compounds are built around the key intermediates
required for this cyclization step.
* To whom correspondence should be addressed. Tel: +32 14
602243. Fax: +32 14 605344. E-mail: fjanssen@prdbe.jnj.com.
† Medicinal Chemistry Department.
‡ General in Vivo Pharmacology Department.
§ CNS-Psychiatry 1 Department.
| Barrier Therapeutics.
10.1021/jm049495j CCC: $30.25 © 2005 American Chemical Society
Published on Web 12/22/2004

Potent, Selective, Nonsedative H1 Antihistamines
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 6 2155
Scheme 1. Synthesis of 1a
a Reagents and conditions: (a) Et3N, CH3CN, reflux; (b) 48% HBr, reflux, 7 h; (c) (CH2O)n, H2, Pd/C, CH3CO2K, NaOH; (d) 60% NaH,
DMF, 60 °C; (e) MeSO3H, 80 °C, 18 h; (f) EtOCOCl, Et3N, toluene, reflux, 2 h; (g) KOH, i-PrOH, reflux, 18 h.
with the acid chloride 6 in the presence of triethylamine
to lead to the cyclization precursor 13, an analogue of
10, used in Scheme 1. In this case, however, the
cyclization under strongly acidic conditions not only
afforded the deprotected compound 1 and its carbamate-
protected derivative 11b but also the N-ethylpiperidine
derivative 14 in a 1:4:3 ratio. The formation of this last
compound could be explained by an alkylation of the
piperidine by ethyl mesylate, produced in situ by acid-
catalyzed hydrolysis of the carbamate 11b.
The preparation of compound 2a is described in
Scheme 3. It was obtained in nine steps from N-
benzylpiperidone with an overall yield of 1.8%. Knoev-
enagel condensation of N-methyl-2-(cyanomethyl)imi-
dazole on N-benzylpiperidone afforded quantitatively
15, the double bond of which was subsequently hydro-
genated to 16 by sodium borohydride in refluxing
2-propanol. After quantitative conversion of the nitrile
16 to the ketone 17 by oxidative decyanation in the
presence of oxygen under phase transfer catalytic condi-
tions,13 rearrangement to 18 occurred in the presence
of trifluoroacetic acid at reflux.14 The one-pot condensa-
tion of 1-bis(ethoxy)methyl imidazole on ketone 18
followed by deprotection quantitatively produced the
carbinol 19 that was immediately dehydrated in the
Figure 1. Structures of new norpiperidine imidazoazepines
presence of trifluoroacetic acid to afford 20a. Alkylation
of 20a by methyl chloroacetate produced the precursor
20b for the key cyclization step. Heating 20b at 120 °C
in trifluoromethanesulfonic acid afforded the required
imidazoazepinone 21, along with its isomer 22 in a 1:1
ratio. Finally, 2b was obtained by catalytic debenzyla-
tion of 21. Over-reduction could not be avoided in this
reaction, and 23 was obtained along with 2b in a 1:1
ratio. All in vitro and in vivo experiments were per-
formed with the fumarate salt (1:1) 2a.
and reference H1 antihistamines selected for evaluation.
Compound 1 was prepared from N-ethoxycarbonyl
isonipecotyl chloride 6 in seven steps with an overall
yield of 28.7% (Scheme 1). Refluxing 1-benzhydrylimi-
dazole with acid chloride 611 led to 7. Deprotection of
both the benzhydryl and the carbamate groups occurred
when 7 was treated with HBr. N-Methylation of the
piperidine 8a, followed by alkylation on the imidazole
8b by the mesylate 912 afforded the precursor for the
cyclization, 10. Cyclization and dehydration leading to
11a took place when 10 was warmed to 80 °C in
methanesulfonic acid. Conversion of the methyl piperi-
dine 11a to a carbamate-protected piperidine 11b fol-
lowed by hydrolysis of 11b finally led to 1. An alterna-
tive preparation for 1 is shown in Scheme 2. This
pathway, although shorter, was less selective. N-Alkyl-
ation of imidazole by the mesylate 9 afforded the
N-(pyrroloethyl)imidazole 12. This compound reacted
The original synthesis of 3a is described in Scheme
4. We prepared 3a in 10 steps from N-benzylpiperidone
in an overall yield of 9.8%. Addition of 1-phenethylimi-
dazole on N-benzylpiperidone afforded 24. This inter-
mediate was then cyclized in the presence of trifluo-
romethanesulfonic acid to the spiroimidazobenzazepine
25a. At this stage, we performed the rest of the
synthesis pathway from the benzyl-protected piperidine
25a (not shown). However, the benzyl-protected inter-

2156 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 6
Scheme 2. Alternative Synthesis of 1a
Janssens et al.
a Reagents and conditions: (a) imidazole, K2CO3, THF, reflux, 72 h; (b) Et3N, CH3CN, reflux; (c) MeSO3H, 80 °C, 2 h.
Scheme 3. Synthesis of 2aa
a Reagents and conditions: (a) MeONa, MeOH, reflux, 4 h; (b) NaBH4, i-PrOH, reflux, 48 h; (c) 50% NaOH, BTEAC, O2 (air), DMSO,
50 °C, 7 h; (d) CF3CO2H, reflux, 5 d; (e) 2.5 M BuLi, i-Pr2NH, THF, -70 °C to rt, then CH3CO2H; (f) CF3CO2H, 0.5 h, reflux; (g) ClCH2CO2Me,
NaH, 50%, DMF, rt, 0.5 h; (h) CF3SO3H, 120 °C, 4 h; (i) H2, Pd/C 10%, MeOH, rt; (j) fumaric acid, EtOH, reflux.
mediates proved difficult to separate by column chro-
matography; this was less of a problem when Boc-
protection was used on the piperidine. Therefore,
debenzylation and subsequent Boc-protection were re-
quired before the next steps could be attempted. 25a
was thus converted to 25c that underwent hydroxy-
methylation to produce 26a, along with its bis(hy-
droxymethyl) analogue 27, in a 2.5:1 ratio. Following
oxidation of 26a by manganese dioxide and conversion
to the ester 26c, standard conditions for hydrolysis and
amide formation led to the protected piperidine 26e.
Finally, deprotection by hydrochloric acid afforded 3a
as a dihydrochloride salt. All in vitro and in vivo
experiments were carried out with this salt 3a.
An alternative pathway, avoiding the tedious func-
tional group interconversions from 25a to 3a, is shown
in Scheme 5. Bromination of 25a with N-bromosuccin-
imide at 0 °C for 1 h led to 28a. The conversion in this
reaction was voluntarily kept low by using a short
reaction time to limit double bromation of the imidazole
ring. A palladium-catalyzed carbon monoxide insertion
on the resulting bromide 28a in the presence of am-
monia led to the amide 28b. Finally, catalytic deben-
zylation provided the free base 3b in five steps and
16.2% overall yield from N-benzylpiperidone. The same
pathway can be followed starting from the Boc-protected
25c, resulting in an improved selectivity toward mono-
bromination and a better yield in the CO insertion

Potent, Selective, Nonsedative H1 Antihistamines
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 6 2157
Scheme 4. Synthesis of 3aa
a Reagents and conditions: (a) 2.5 M BuLi, i-Pr2NH, THF, -78 to 0 °C; (b) CF3SO3H, 65 °C, 120 h; (c) H2, 10% Pd/C, MeOH; (d)
(Boc)2O, CH2Cl2; (e) 37% CH2O, AcONa, AcOH; (f) MnO2, CHCl3; (g) NaCN, MnO2, AcOH, MeOH; (h) 1 N NaOH, THF/H2O; (i) NH4Cl,
EDCI, Et3N, DMAP, CH2Cl2; (j) HCl, MeOH, i-PrOH.
Scheme 5. Synthesis of 3ba
a Reagents and conditions: (a) NBS, CH2Cl2, 0 °C, 1 h; (b) CO, NH3, Pd(OAc)2, 1,3-bis(diphenylphosphino)propane; (c) H2, 10% Pd/C,
MeOH.
Table 1. Experimental Physicochemical Properties of the Title
reaction (not shown). The resulting 26e could then also
Compounds and of the Reference Compounds Loratadine (4)
be deprotected to give directly the dihydrochloride salt
3a as shown in Scheme 4.
and Cetirizine (5)
solubility
in H2O,
mg/mL
log
c
a
b
b
compd MW
log Poct
pKa1
pKa2
D7.4
Physicochemical Properties
1
268.36 1.25
9.85
NDd
9.88
6.52
-1.2 NDd
The physicochemical properties of antihistamines
have a profound influence on their side-effect profile.1b
They not only determine the bioavailability of the
compounds but also the brain penetration responsible
for the sedation observed with first-generation antihis-
tamines. Table 1 gives an overview of the properties that
have been determined for the title compounds and
compares them with the reference antihistamines lora-
tadine (4) and cetirizine (5). The log D7.4 values were
calculated based on the log Poct and pKa1 values mea-
sured for the compounds. The low log Poct values of
compounds 1 and 3a led to low log D7.4 values that are
an indication for negligible brain penetration.1b The
solubility of 3a in water is also shown in Table 1.
Although we did not directly compare the title com-
pounds with loratadine (4) and cetirizine (5), it is clear
that 3a has a high solubility when dissolved in water.
Table 2 shows that the solubility of 3a was still higher
than 20 mg/mL in water at pH 7 (resulting in a solution
2a
3a
4
282.35 NDd
296.37 1.18
382.89 4.86
NDd
3.00
NDd
-1.3 >20e-g
4.5815
4.58
0.0116 h
5
388.89 1.01-1.5017 8.0017 2.19-2.9317 1.517 10016 h
a Octanol/pH 12 buffer. b Sirius PCA 101 method. c Calculated
using the formula log D7.4 ) log P - log(1 + 10pK -7.4). d Not
a
determined. e See Experimental Section for details of the method.
f All compound put into solution during the test was dissolved.
g Solution pH ) 2.0. h Solution pH not available.
of pH 2) and still exceeded that value in buffer solutions
up to pH 4.3. The free base 3b also had a solubility
higher than 20 mg/mL at acidic pH, while its solubility
decreased to around 10 mg/mL, in buffer solutions
between pH 6 and 8, and 1.1 mg/mL in water (resulting
in a solution of pH 10.5).
Pharmacology
In Vitro Pharmacology. The antihistaminic activity
of the compounds was evaluated in vitro in a receptor

2158 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 6
Janssens et al.
Table 5. Inhibition of Histamine-Induced Lethalitya in the
Table 2. Solubilitya of 3a and Its Free Base 3b in Aqueous
Medium at 20 °C
Guinea Pig
3a
3b
ED50, mg/kg (95% CLb),
compd
3 h after po administration
pH of
solubility,
pH of
solubility,
solvent
water
solution
mg/mL
solution
mg/mL
1
0.67 (0.50-0.91)c
2a
0.019 (0.012-0.030)
0.074 (0.050-0.11)
0.074 (0.055-0.10)
0.032 (0.024-0.044)
2.0
1.0
1.1
2.3
1.8
2.9
4.2
3.8
4.3
12.6
>20b
>20b
>20b
>20b
>20b
>20b
>20b
>20b
>20b
3.09
10.5
2.7
3.1
1.1
>20b
>20b
1.69
3a
0.1 M HCl
loratadine (4)
cetirizine (5)
SGFc
SIFd
10.1
4.8
buffer, pH 2
buffer, pH 4
buffer, pH 6
buffer, pH 8
buffer, pH 10
0.1 M NaOH
>20b
>20b
8.04
a Intravenous injection of histamine induces a lethal shock in
the guinea pig. Antihistamines were given orally (po). b Confidence
limits. c Tested 1 h after po administration
5.4
9.2
9.0
12.22
1.65
0.93
10.2
13.0
order of magnitude less potent (Table 5). All compounds
showed a rapid onset of action, within 30-45 min (rat)
or 60-72 min (guinea pig) (results not shown). In the
rat, 3a, loratadine (4) and cetirizine (5) showed a similar
duration of action (4.5-7 h), whereas in the guinea pig,
3a showed a prolonged duration of action (33 h) in
comparison with loratadine (9 h) or cetirizine (6 h)
(results not shown).
a See Experimental Section for details of the method. b All
compound put into solution during the test was dissolved. c SGF:
simulated gastric fluid. d SIF: simulated intestinal fluid.
Table 3. Receptor Binding Affinities for the Human Cloned
Histamine H1 Receptor
compd
Ki (nM)a
compd
Ki (nM)a
1
2a
3a
22
12
19
loratadine (4)
cetirizine (5)
37
50
In subsequent experiments, all compounds were
tested for their effect on cutaneous reactions in the rat,21
the guinea pig, and the dog.25
a Human H1 receptor cloned and expressed in CHO cells.
In the rat, skin reactions were induced by histamine,
serotonin, Ascaris allergens, and a passive cutaneous
reaction (PCA) to ovalbumin. ED50s for inhibition and
blockade of the skin reactions were obtained 2 h after
the subcutaneous injection of the compounds (see the
Experimental Section). All compounds dose-dependently
inhibited and, at slightly higher doses, blocked the
histamine-, PCA- and Ascaris allergens-induced reac-
tions (Table 6). ED50s for inhibition and blockade of
histamine reaction, as well as blockade of PCA and
Ascaris reaction, were comparable for all compounds
tested, except for 1, which was clearly more potent in
inhibiting the cutaneous reactions to the various stimuli.
Blockade of the histamine reaction occurred for all
compounds at doses several times higher than the dose
required to inhibit the compound 48/80-induced lethality
after subcutaneous administration (factors ranging from
4.6 to 26), except for cetirizine (5) (factor 1.3). Of the
tested compounds, only loratadine (4) at high doses
showed some activity against the serotonin-induced
reaction.
In the guinea pig, skin reactions were induced by
histamine, substance P, Ascaris allergens, bradykinin,
and platelet-activating Factor (PAF). All tested com-
pounds, dose-dependently inhibited and, at higher
doses, blocked the histamine reaction (Table 7). In
contrast to the results in the rat, 1 was the least potent
compound in antagonizing the cutaneous reactions to
histamine and Ascaris allergens in the guinea pig. The
ED50 of 3a for complete blockade of the histamine
reaction was only slightly higher than for inhibition of
the histamine reaction (factor 1.4), whereas for the other
compounds, a slightly larger difference was observed
(factor 3-4). Inhibition of histamine-induced skin reac-
tions occurred at doses closely related to those required
for protection against histamine-induced lethality (see
Table 5). Compounds 1, 2a, 3a and loratadine (4) tended
to inhibit the Ascaris allergens-induced reaction at high
doses, exceeding their inhibitory antihistamine doses by
a factor 36, 21, 12, and 5, respectively. Cetirizine (5)
did not influence the Ascaris allergens-induced reaction
Table 4. Inhibition of Compound 48/80-Induced Lethalitya in
the Rat
ED50, mg/kg (95% CLb)
1 h after sc
administration
2 h after po
administration
compd
1
2a
3a
0.028 (0.019-0.042)
0.037 (0.023-0.060)
0.056 (0.033-0.097)
0.29 (0.20-0.44)
0.76 (0.51-1.2)
0.34 (0.21-0.55)
1.2 (0.72-1.9)
0.22 (0.15-0.33)
1.2 (0.78-1.8)
loratadine (4)
cetirizine (5)
0.51 (0.32-0.82)
a Intravenous injection of compound 48/80 induces a lethal
anaphylactic reaction. Antihistamines were given either subcu-
taneously (sc) or orally (po). b Confidence limits.
binding test with the human cloned H1 histamine
receptor, expressed in CHO cells.18 Results are sum-
marized in Table 3. All three title compounds displaced
the radioligand from the receptor with a Ki ranging from
12 to 22 nM. In this respect, the title compounds showed
an affinity for the H1 receptor on the same order of
magnitude as loratadine (4) (37 nM) and cetirizine (5)
(50 nM).
In Vivo Antihistaminic Activity. The in vivo an-
tihistaminic activity of the compounds was first evalu-
ated in the compound 48/80-induced lethality test in
rats19 and the histamine-induced lethality test in guinea
pigs20 after subcutaneous and/or oral administration.
All compounds dose-relatedly protected against lethal
anaphylactic shock after injection of compound 48/80 in
the rat (Table 4). The three title compounds were more
potent than the reference compounds cetirizine and
loratadine when administered subcutaneously. After
oral administration, however, compounds 1, 2a, and 3a
were several times less potent than after sc injection,
whereas loratadine (4) and cetirizine (5) were about
equipotent when administered by both routes in the rat.
After oral administration, all tested compounds thus
showed a comparable potency. In the guinea pig, all
compounds exhibited a similar potency against hista-
mine-induced lethal shock, except for 1, which was 1

Potent, Selective, Nonsedative H1 Antihistamines
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 6 2159
Table 6. Cutaneous Reaction Induced by Several Mediators in the Rata
ED50, mg/kg (95% CLb)
histamine
PCA
Ascaris allergens
serotonin
inhibition
>0.16
compound
inhibition
blockade
blockade
blockade
1
0.080
(0.046-0.14)
0.55
0.13
(0.057-0.28)
0.95
(0.42-2.13)
1.4
(0.84-2.2)
1.8
(1.2-2.7)
0.68
(0.45-1.1)
0.080
(0.046-0.14)
0.42
(0.14-1.23)
2.3
0.13
(0.057-0.28)
2.9
2a
>10
>10
(0.24-1.2)
0.51
(1.1-7.5)
3a
2.7c
(0.30-0.88)
0.89
(0.72-1.1)
0.68
(0.45-1.1)
(1.3-4.3)
1.6
loratadine (4)
cetirizine (5)
2.7
(1.7-4.3)
3.6c
6.2
(4.1-9.2)
>10
(0.90-2.7)
2.7c
a Skin reactions were induced by histamine, passive cutaneous anaphylaxis (PCA), Ascaris allergens, or serotonin. Antihistamines
were given subcutaneously 2 h before skin challenge. Results are expressed as ED50 (mg/kg). b Confidence limits. c Nonlinear dose-
response: confidence limits have not been calculated.
Table 7. Cutaneous Reactions Induced by Several Mediators in the Guinea Piga
ED50, mg/kg (95% CLb)
histamine
Substance P
inhibition
Ascaris allergens
compd
inhibition
blockade
inhibition
1
0.24
(0.11-0.54)
0.020
(0.008-0.045)
0.10
(0.057-0.19)
0.080
(0.036-0.18)
0.046
(0.025-0.084)
0.96
(0.52-1.8)
0.080
(0.036-0.18)
0.14
(0.076-0.25)
0.32
(0.14-0.71)
0.14
(0.062-0.31)
1.7
(0.56-4.9)
>2.5
8.7
(4.8-16)
0.42
2a
3a
(0.18-0.93)
1.6c
2.2c
1.2c
loratadine (4)
cetirizine (5)
0.42
(0.14-1.3)
>2.5
>2.5
a Skin reactions were induced by intradermal application of histamine, substance P, or Ascaris allergens. Antihistamines were given
orally 2 h before intradermal challenge. b Confidence limits. c As, at the highest dose of 2.5 mg/kg, effect was observed in only 60% of the
animals tested, confidence limits were not calculated.
Table 8. Protection against Ascaris Allergens-Induced
up to 54 times its antihistamine dose (>2.5 mg/kg).
Cutaneous Reactionsa in Dogs
Similarly to the Ascaris allergens-induced reaction,
peak-effect
dose, ED50
mg/kg
compounds 1, 3a, and loratadine (4) tended to inhibit
,
onset of
duration
the substance P-induced cutaneous reactions, at several
times the doses required for inhibition of the histamine
reaction (7, 16, and 28 times, respectively). Cetirizine
(5) and 2a were devoid of activity against substance P
up to 2.5 mg/kg (54 and 125 times their antihistamine
dose, respectively). None of the compounds were able
to suppress the substance P reaction to the level of
pronounced inhibition. All compounds were devoid of
anti-bradykinin or anti-PAF activity in the skin, up to
doses of 2.5 mg/kg (10 mg/kg for 1) (results not shown).
After oral administration in the dog, the title com-
pounds as well as loratadine (4) and cetirizine (5) dose-
dependently inhibited the cutaneous reaction induced
by Ascaris allergens. In terms of peak-effect dose, the
title compounds were more potent than either loratadine
(5-11 times) or cetirizine (4-8 times). All compounds
showed a similar rapid onset of action (within 1 h), but
at 4 times the ED50 values, the reference compounds
and 1 had a longer duration of action (∼30 h) than 3a
(21 h) or 2a (13 h). Peak effect was reached for all
compounds 4 h after oral administration. At the maxi-
mal antihistamine effect, the Ascaris allergens-induced
reaction was inhibited to a maximum of 20% of the
control. Increasing the doses of the antihistamines did
not further reduce the Ascaris allergens-induced skin
reactions.
compd
actionb (h)
of actionb (h)
1
2a
3a
0.038
0.018
0.024
0.20
<1
<1
<1
<1
<1
35
13
21
33
30
loratadine (4)
cetirizine (5)
0.14
a Skin reactions were induced by intradermal application of
Ascaris allergens. Antihistamines were orally administered. b On-
set and duration of action were graphically estimated at four times
the peak-effect dose.
good estimate of the sedative potential of H1 antihista-
mines.23 We evaluated the central H1 receptor oc-
cupancy ex vivo by quantitative autoradiography 3 h
after oral administration of the compounds. Preliminary
experiments indicated that 3a did not significantly bind
to the central H1 receptor of the guinea pig up to a dose
of 10 mg/kg, exceeding the dose (ED50) required to
protect from the histamine-induced lethality in the same
species by a factor >135. For 1 and 2a, selectivity ratios
of 64 and 125, respectively, were obtained. Loratadine
showed a selectivity ratio of only 30. As, based on these
experiments, 3a appeared to be the least sedative
compound, it was compared in more detail with lorata-
dine. Compound 3a did not occupy significantly the
central H1 receptors in the guinea pig up to 40 mg/kg,
exceeding the dose necessary to protect from histamine
lethality by a factor larger than 540, and the dose
Penetration into the CNS. Occupancy of central H1
receptors in the cerebellum of the guinea pig gives a

2160 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 6
Janssens et al.
needed to block the histamine-induced cutaneous reac-
tion by a factor greater than 285. On the other hand,
loratadine already occupied 50% of the central H1
receptors at a dose of 2.2 mg/kg, which corresponds to
30 times the dose needed to protect from histamine
lethality in the guinea pig and only 7 times the dose
effective against cutaneous histamine reactions in this
species. These results were corroborated by EEG power
spectral analysis24 in the awake rat, showing that 3a
had no sedative activity in this model (results not
shown, will be published elsewhere). Compound 3a thus
appears to be devoid of central sedative effects.
Electrophysiological Cardiovascular Safety. An-
tihistamines are usually regarded as a class of com-
pounds with a potential for inducing electrophysiological
effects that may occasionally trigger life-threatening
cardiac arrhythmias (Torsades de Pointes) in humans.25
Such effects include the inhibition of the rapidly acti-
vating component of the delayed rectifier potassium
current (IKr), prolongation of the action potential in
isolated cardiac tissue, and prolongation of the QT-
interval of the electrocardiogram in animals and/or
humans.
Voltage clamp tests on human embryonic kidney
(HEK-293) cells transfected with the human ether-a-
go-go related gene (HERG), expressing the IKr-like
outward potassium current modulating repolarization
in cardiac cells, showed that 3a, 1, and 2 did not reduce
the IKr-like current at concentrations of 3 × 10-8 and
3 × 10-7 M. At 3 × 10-7 M the observed marginal
reductions for 3a, 1, and 2 were 1%, 2%, and 5%,
respectively. Even at high concentrations of 3 × 10-6
and 10-5 M, 3a did not induce a significant reduction
of the IKr-like current (3% and 8%, respectively) when
compared to control conditions (2.3%). In comparison,
it has been reported that astemizole and terfenadine
potently blocked the IKr-like current with IC50 values
of (0.9-1.5) × 10-9 26 and 50 × 10-9 M,6f respectively.
dependent decrease in heart rate (starting at a total
dose of 0.48 mg/kg) and an increase in QT and QTcB
(starting at a total dose of 0.16 mg/kg). Terfenadine also
significantly decreased heart rate (starting at a total
dose of 4.85 mg/kg) and prolonged the QT and QTcB
(starting respectively at a total dose of 2.35 and 0.47
mg/kg).
Conclusion
We described the synthesis and biological activity of
three new norpiperidine imidazoazepines representative
of a new class of H1 antihistaminic compounds. The
three title compounds were characterized as potent and
selective H1 antihistamines, in vitro as well as in vivo.
In this respect, the compounds were at least as potent
as the reference compounds cetirizine (5) and loratadine
(4). However, in relation to potential sedation, the title
compounds were less prone to penetrate the central
nervous system than the reference compounds. Com-
pound 3a was even completely devoid of interaction with
central H1 receptors, suggesting absence of sedative
side-effect liability. In vitro cardiovascular screening
tests showed that 3a lacked the intrinsic capacity to
influence the IKr membrane ion flux or to modulate the
action potential characteristics in cardiac cells at con-
centrations up to 10-5 M. Furthermore, in vivo safety
pharmacology studies in anaesthetized guinea pigs
indicate that systemic administration of 3a at high
doses had no intrinsic potential to prolong the QT-
interval. Taking all these preclinical evaluations into
consideration, we have selected 3a for further clinical
development, mainly in the field of dermatological
disorders. This compound will be a suitable tool to
explore the activity of a selective H1 antihistamine in
various indications, without the contamination of the
sedative activity often observed with other marketed
antihistamines when increasing doses.
Experimental Section
In isolated guinea pig papillary muscle stimulated at
a normal rhythm of 60 pulses/min and under normokale-
mic conditions (4 mM KCl), 3a, at concentrations up to
10-5 M, had no relevant effect on the duration of the
action potential. The observed changes were less than
10% versus baseline. Compound 3a did not elicit mor-
phological changes such as early and delayed afterde-
polarizations, indicating the absence of proarrhythmic
effects in this preparation. In comparison, in the same
model, astemizole and terfenadine significantly pro-
longed the action potential in isolated papillary muscles
already at concentrations of 3 × 10-8 and 10-7 M,
respectively.
In anaesthetized guinea pigs treated with 3a at
cumulative iv bolus doses of 0.08, 0.16, 0.32, 0.64, 1.25,
and 5 mg/kg, administered at 15 min intervals (total
dose ) 7.45 mg/kg iv in 75 min), 3a had no statistically
significant effect on heart rate, mean arterial blood
pressure, and the duration of the PQ-, QRS- and QT-
interval. No changes in ECG morphology were noticed
during the post-treatment period. Relative to solvent,
3a, starting from 0.64 mg/kg iv, slightly decreased the
duration of the QTc-interval corrected according to
Bazett (QTcB; max effect +2% at 1.25 mg/kg iv versus
+7% with solvent; p < 0.05). In comparison, in the same
model, astemizole induced a significant and dose-
General Methods. Loratadine (4) and cetirizine (5) were
obtained from commercial sources. Unless otherwise stated,
all reactions were carried out in dry apparatus under an
atmosphere of dry nitrogen. Commercially available absolute
solvents were used. Column chromatography was carried out
using Merck silica gel 60 (70-230 mesh). Caution! Methane-
sulfonic acid and trifluoromethanesulfonic acid, used in the
syntheses of 1, 11a, 11b, 14, 21, 22 and 25a are extremely
corrosive substances. All procedures using these reagents must
be carefully executed wearing all appropriate personal protec-
tion.
1H and 13C NMR spectra were recorded on a 400 MHz
spectrometer (Bruker) using CDCl3 or DMSO-d6 as internal
1
standard. H NMR and 13C NMR data for the intermediates
are listed in the Supporting Information. Elemental analysis
were carried out on a CarloErba EA1110. Melting points were
determined on a Mettler, a Bu¨chi 545, and a Ko¨fler apparatus
and are uncorrected.
Ethyl 4-[[1-Benzyl-1H-imidazol-2-yl]carbonyl]-1-pip-
eridinecarboxylate (7). A mixture of N-benzhydrylimidazole
(235 g, 1 mol) and triethylamine (132 g, 1.3 mol) in acetonitrile
(1250 mL) was stirred at 20 °C. N-Ethoxycarbonyl isonipecotyl
chloride11 6 (264 g, 1.2 mol) was added dropwise (exother-
mic: temperature rose to 34 °C). Precipitation occurred. The
reaction mixture was stirred for 4 h at reflux. The reaction
mixture was cooled to room temperature and poured out into
a 50% sodium hydroxide solution (160 mL). The mixture was
concentrated and extracted with dichloromethane. The organic
layer was washed with water, separated, dried on sodium

Potent, Selective, Nonsedative H1 Antihistamines
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 6 2161
sulfate, and filtered, and the solvent was evaporated. Recrys-
tallization from methylisopropyl ketone afforded 404 g of 7
(97%). Mp: 122.9 °C. Anal. (C25H27N3O3): C, H, N.
(1H-Imidazol-2-yl)(4-piperidinyl)methanone Dihydro-
bromide (8a). 7 (387.3 g, 0.93 mol) and 48% hydrobromic acid
(1700 mL) were stirred and refluxed for 7 h. The mixture was
evaporated and the residue was boiled in 2-propanol, filtered,
and dried to afford 282.3 g of 8a (92%). This compound was
used in the next step without further purification.
(1H-Imidazol-2-yl)(1-methyl-4-piperidinyl)methan-
one (8b). A mixture of 8a (141.2 g, 0.416 mol), potassium
acetate (100 g, 1.02 mol), and paraformaldehyde (22 g, 0.73
mol) in methanol (700 mL) was hydrogenated at 50 °C with
Pd/C 10% (5 g) as a catalyst in the presence of a 4% solution
of thiophene in diisopropyl ether (10 mL). After uptake of
hydrogen (1 equiv), the catalyst was filtered off and the filtrate
was evaporated. The residue was dissolved in water (100 mL).
A 25% ammonia solution (150 mL) was added dropwise while
cooling. The water layer was saturated with potassium car-
bonate and extracted with dichloromethane. The organic layer
was separated, dried on magnesium sulfate, and filtered, and
the solvent was evaporated. The residue was stirred in
diisopropyl ether. The solid was filtered off and dried, yielding
80.5 g of 8b (100%). Mp: 143.6 °C. Anal. (C10H15N3O): C, H,
N.
5,6,7,10-Tetrahydro-7-methyl-10-(4-piperidinylidene)-
imidazo[1,2-a]pyrrolo[3,2-d]azepine (1). A mixture of 11b
(54.0 g, 0.165 mol) and potassium hydroxide (92.4 g, 1.65 mol)
in 2-propanol (1000 mL) was stirred and refluxed overnight.
After evaporation of the solvent, the residue was taken up in
water and extracted with dichloromethane. The organic layer
was dried, filtered, and evaporated. The residue was crystal-
lized from ethyl acetate, yielding 28.1 g of 1 (63%). Mp: 194.8
°C. 1H NMR (400 MHz): δ 2.60 (t, J ) 5.7 Hz, 2 H), 2.73 (t, J
) 5.7 Hz, 2 H), 2.90 (m, 6 H), 3.44 (s, 3 H), 4.32 (m, 2 H), 6.04
(d, J ) 2.8 Hz, 1 H), 6.50 (d, J ) 2.8 Hz, 1 H), 6.85 (d, J ) 1.3
Hz, 1 H), 6.92 (d, J ) 1.3 Hz, 1 H); 13C NMR (101 MHz) δ
27.3, 32.5, 32.9, 33.6, 42.9, 47.9, 48.2, 109.2, 117.1, 118.1, 118.2,
120.0, 126.2, 126.4, 140.9, 150.2. Anal. (C16H20N4): C, H, N.
1-[2-(1-Methyl-1H-pyrrol-2-yl)ethyl]-1H-imidazole (12).
A mixture of 9 (17.8 g, 0.086 mol), imidazole (11.7 g, 0.172
mol), and potassium carbonate (14 g, 0.1 mol) in tetrahydro-
furan (400 mL) was stirred and refluxed for 72 h. After cooling,
the reaction mixture was evaporated and the residue was
stirred in water. The mixture was extracted with dichlo-
romethane and the separated organic layer was dried on
magnesium sulfate, filtered, and evaporated. Purification by
column chromatography over silica gel (eluent: dichlo-
romethane/methanol 95/5) afforded 9.3 g of 12 (62%) that was
used without further purification in the next step.
Ethyl 4-[[1-[2-(1-Methyl-1H-pyrrol-2-yl)ethyl]-1H-imi-
dazol-2-yl]carbonyl]-1-piperidinecarboxylate (13). N-
Ethoxycarbonyl isonipecotyl chloride11 6 (34.8 g, 0.159 mol)
was added dropwise to a cooled mixture (ice bath) of 12 (9.3 g,
0.053 mol) and triethylamine (19 g, 0.19 mol) in acetonitrile
(150 mL). The reaction mixture was stirred for 2 h at room
temperature and for 4 h at reflux temperature. Stirring was
continued overnight at room temperature. A sodium hydroxide
50% solution (16 mL) was then added dropwise. After stirring
and refluxing for 30 min, the reaction mixture was concen-
trated. The residue was stirred in water and the mixture was
extracted with dichloromethane. The separated organic layer
was dried on magnesium sulfate, filtered, and evaporated to
afford 25 g of 13 (100%) that was used in the next step without
further purification.
5,6,7,10-Tetrahydro-7-methyl-10-(4-piperidinylidene)-
imidazo[1,2-a]pyrrolo[3,2-d]azepine (1), Ethyl 4-(5,6-Di-
hydro-7-methyl-10(7H)-imidazo[1,2-a]pyrrolo[3,2-d]-
azepin-10-ylidene)-1-piperidinecarboxylate (11b), and
10-(1-Ethyl-4-piperidinylidene)-5,6,7,10-tetrahydro-7-
methylimidazo[1,2-a]pyrrolo[3,2-d]azepine (14). A mix-
ture of 13 (71 g, 0.2 mol) in methanesulfonic acid (1800 mL)
was stirred at 80 °C overnight. The mixture was poured into
ice/sodium hydroxide, to keep the temperature below 30 °C,
and was extracted with dichloromethane. The organic layer
was dried on magnesium sulfate, filtered, and evaporated.
Column chromatography over silica gel (eluent: dichlo-
romethane/(ammonia/methanol 7 N) 95/5 to 90/10) afforded
33.4 g of 11b (49%), 6 g of 1 (11%), and 20 g of 14 (34%). For
analytical purposes, a sample of 14 (1.5 g) was converted into
its fumarate salt (1:1) in ethanol. The analytical data reported
below are those of this salt. Mp: 200.9 °C. Anal. Calcd for
C18H24N4·C4H4O4: C, 64.06; H, 6.84; N, 13.58. Found: C, 63.34;
H, 6.88; N, 13.31.
(1-Methyl-4-piperidinyl)[1-[2-(1-methyl-1H-pyrrol-2-yl)-
ethyl]-1H-imidazol-2-yl]methanone (10). Dimethyl forma-
mide (800 mL) was stirred under nitrogen flow. Sodium
hydride (60% in paraffin) (21.98 g, 0.55 mol) was added
portionwise. 8b (80.5 g, 0.416 mol) was added portionwise and
this mixture was stirred for 2 h at room temperature. A
solution of the mesylate 912 (92.9 g, 0.457 mol) in dimethyl
formamide was added dropwise. The reaction mixture was
stirred overnight at 60 °C. The reaction mixture was cooled
and quenched with water while cooling. This mixture was
extracted with dichloromethane. The organic layer was sepa-
rated, dried on magnesium sulfate, and filtered, and the
solvent was evaporated. Column chromatography over silica
gel (eluent: dichloromethane/methanol 95/5 increasing to
dichloromethane/(ammonia/methanol 7 N) 90/10) afforded 94.7
g of 10 (76%) after recrystallization in diisopropyl ether. Mp:
89.8 °C. Anal. (C17H24N4O): C, H, N.
5,6,7,10-Tetrahydro-7-methyl-10-(1-methyl-4-piperidi-
nylidene)imidazo[1,2-a]pyrrolo[3,2-d]azepine (11a). This
reaction was performed in three batches. Methanesulfonic acid
(3 × 1600 mL) was added portionwise to 10 (3 × 60.68 g, 3 ×
0.202 mol) cooled on an ice bath, and the mixture was stirred
at room temperature. The mixture was warmed to 80 °C and
stirred at this temperature overnight. The mixture was cooled,
poured onto ice, alkalized with sodium hydroxide, and ex-
tracted with dichloromethane. The organic layer was sepa-
rated, dried on magnesium sulfate, and filtered. The three
batches were combined and evaporated. After purification by
column chromatography over silica gel (eluent: dichlorometh-
ane/(ammonia/methanol 7 N) 96/4 to 90/10), the product was
suspended in methylisopropyl ketone, filtered, and dried at
60 °C under vacuum overnight to afford 92.8 g of 11a (80%).
Mp: 190.0 °C. Anal. (C17H22N4): C, H, N.
(1-Benzylpiperidin-4-ylidene)(1-methyl-1H-pyrrol-2-
yl)acetonitrile (15). A mixture of N-benzylpiperidone (261
g, 1.38 mol), (1-methyl-1H-pyrrol-2-yl)acetonitrile (150 g, 1.23
mol), and sodium methanolate 30% in methanol (230 mL) was
refluxed in methanol (900 mL) for 12 h. The solvent was
evaporated and the residue was dissolved in water and
extracted with dichloromethane. The organic layer was dried
on magnesium sulfate, filtered, and evaporated to quantita-
tively produce 365 g of 15 that was used in the next step
without further purification.
r-(1-Methyl-1H-pyrrol-2-yl)-1-benzyl-4-piperidineace-
tonitrile (16). A mixture of 15 (365 g, 1.25 mol) in 2-propanol
(1600 mL) was stirred and warmed to 40 °C. Sodium borohy-
dride (95 g, 2.5 mol) was added portionwise over 15 min and
the mixture was refluxed for 48 h. After cooling, water was
Ethyl 4-(5,6-Dihydro-7-methyl-10(7H)-imidazo[1,2-a]-
pyrrolo[3,2-d]azepin-10-ylidene)-1-piperidinecarboxy-
late (11b). A mixture of 11a (8.47 g, 0.03 mol) and triethyl-
amine (6.07 g, 0.06 mol) in toluene (300 mL) was stirred and
refluxed. Ethyl chloroformate (16.28 g, 0.15 mol) was added
dropwise and the mixture was refluxed for 2 h. After cooling,
water was added and the mixture was neutralized with
potassium carbonate. The organic layer was separated and the
aqueous layer was further extracted with chloroform. The
combined organic layers were evaporated. Column chroma-
tography over silica gel (eluent: dichloromethane/methanol 90/
10) gave 11 g of solid product. This residue was boiled up in
2-propanone, filtered, and dried to afford 8.58 g of 11b (84%).
Mp: 232.0 °C. Anal. Calcd for C19H24N4O2: C, 67.04; H, 7.11;
N, 16.46. Found: C, 66.38; H, 7.14; N, 16.33.

2162 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 6
Janssens et al.
added and the mixture was extracted with diisopropyl ether.
The organic layer was dried on magnesium sulfate, filtered,
and evaporated. The residue was recrystallized from diisopro-
pyl ether, yielding 294 g of 16 (80%). Mp: 105.5 °C. Anal.
(C19H23N3): C, H, N.
in water, sodium bicarbonate (10 g) was added, and the
mixture was extracted with dichloromethane. The organic
layer was dried on magnesium sulfate, filtered, and evapo-
rated. Column chromatography over silica gel (eluent: dichlo-
romethane/methanol 96/4) afforded 65 g of 20b (73%) that was
used without further purification in the next step.
7,10-Dihydro-7-methyl-10-[1-(phenylmethyl)-4-piper-
idinylidene]imidazo[1,2-a]pyrrolo[3,2-d]azepin-6(5H)-
one (21) and 8,10-Dihydro-8-methyl-10-[1-benzyl-4-pip-
eridinylidene]imidazo[1,2-a]pyrrolo[3,4-d]azepin-6(5H)-
one (22). A mixture of 20b (65 g, 0.16 mol) in trifluoro-
methanesulfonic acid (650 mL) was stirred at 120 °C for 4 h.
The mixture was cooled, poured into ice/potassium carbonate/
water, and extracted with dichloromethane. The organic layer
was dried on magnesium sulfate, filtered, and evaporated.
Column chromatography over silica gel (eluent: dichlo-
romethane/methanol 96/4) afforded fractions 1 and 2. These
were recrystallized from acetonitrile, respectively yielding 11.3
g of 21 [Yield: 19%. Mp: 213.5 °C. Anal. (C23H24N4O): C, H,
N.] and 11 g of 22 [Yield: 18%. Mp: 175.1 °C. Anal.
(C23H24N4O): C, H, N.].
7,10-Dihydro-10-(4-piperidinylidene)imidazo[1,2-a]py-
rrolo[3,2-d]azepin-6(5H)-one Fumarate Salt (2a) and
7,10-Dihydro-10-(4-piperidinyl)imidazo[1,2-a]pyrrolo-
[3,2-d]azepin-6(5H)-one (23). A mixture of 21 (13.8 g, 0.037
mol) in methanol (150 mL) was hydrogenated at room tem-
perature (atmospheric pressure) with Pd/C 10% (2 g) as a
catalyst. After uptake of hydrogen (0.7 equiv), the catalyst was
filtered off and the filtrate was evaporated. Column chroma-
tography over silica gel (eluent: dichloromethane/methanol/
(ammonia/methanol 7 N) 90/5/5 to 90/0/10) afforded 2a (5.3 g,
51%) and 23 (5.1 g, 49%). For analytical purposes, a sample
of each compound was converted to its fumarate salt (1:1). The
analytical data reported below are those of these salts.
Compound 2a. Mp: 250 °C (Kofler). 1H NMR (360 MHz,
DMSO-d6): δ 2.70 (m, 2 H), 2.78 (m, 2 H), 2.93 (m, 2 H), 3.12
(m, 1 H), 3.22 (m, 1 H), 3.84 (s, 3 H), 4.69 (d, J ) 16.1 Hz, 1
H), 5.07 (d, J ) 16.0 Hz, 1 H), 6.22 (d, J ) 2.5 Hz, 1 H), 6.46
(s, 2 H), 6.82 (d, J ) 1.2 Hz, 1 H), 7.25 (d, J ) 2.5 Hz, 1 H),
7.28 (d, J ) 1.2 Hz, 1 H). Anal. (C16H18N4O·C4H4O4): C, H, N.
Compound 23. Mp: 243.5 °C. Anal. Calcd for C16H20N4O·
C4H4O4: C, 59.99; H, 6.04; N, 13.99. Found: C, 59.53; H, 6.12;
N, 13.90.
4-[1-(2-Phenylethyl)-1H-imidazol-2-yl]-1-benzyl-4-pip-
eridinol (24). A mixture of diisopropylamine (142 g, 1.4 mol)
in tetrahydrofuran (3000 mL) was stirred at -70 °C. Butyl-
lithium (2.5 M) in hexanes (520 mL, 1.3 mol) was added
portionwise at a temperature below -40 °C. The mixture was
stirred at -70 °C for 15 min. 1-Phenethylimidazole (172 g, 1
mol) dissolved in tetrahydrofuran was added dropwise at a
temperature below -55 °C. The mixture was stirred at -70
°C for 1 h. N-benzylpiperidone (227 g, 1.2 mol) dissolved in
tetrahydrofuran was added dropwise at a temperature below
-55 °C. The mixture was stirred at -70 °C for 1 h and then
brought to room temperature, stirred at room temperature
overnight, and quenched with water. The organic solvent was
evaporated. The aqueous concentrate was extracted with
dichloromethane. The organic layer was separated, dried on
magnesium sulfate, and filtered, and the solvent was evapo-
rated. Crystallization of the residue from diisopropyl ether
(1100 mL) afforded 271 g of 24 (75%). Mp: 110.5 °C. Anal.
(C23H27N3O): C, H, N.
(1-Methyl-1H-pyrrol-2-yl)[1-benzyl-4-piperidinyl]meth-
anone (17). A mixture of 16 (250 g, 0.99 mol), sodium
hydroxide 50% solution (96 g, 1.2 mol), and benzyltriethylam-
monium chloride (10 g, 0.054 mol) in dimethyl sulfoxide (800
mL) was stirred at room temperature. Air was bubbled through
the mixture for 7 h (the temperature spontaneously raised to
50 °C). After cooling, the mixture was poured into water (3000
mL) and extracted with methyl isopropyl ketone. The organic
layer was washed with water, dried on magnesium sulfate,
filtered, and evaporated, quantitatively yielding 280 g of 17.
For analytical purposes, a sample of 17 was converted to its
fumarate salt (1:1) in ethanol. The analytical data reported
below are those of this salt. Mp: 183.0 °C. Anal. Calcd for
C18H22N2O·C4H4O4: C, 66.32; H, 6.58; N, 7.03. Found: C, 65.82;
H, 6.53; N, 6.99.
(1-Methyl-1H-3-pyrrolidinyl)[1-benzyl-4-piperidinyl]-
methanone (18). A mixture of 17 (275 g, 0.97 mol) in
trifluoroacetic acid (2000 mL) was stirred and refluxed for 5
days. After concentration, the residue was poured out into ice/
water/potassium carbonate and extracted with dichloromethane.
The organic layer was dried on magnesium sulfate and filtered,
and the solvent was evaporated. Column chromatography over
silica gel (eluent: dichloromethane/methanol 95/5) followed by
crystallization from acetonitrile afforded 121 g of 18 (44%).
Mp: 145.3 °C. Anal. (C18H22N2O): C, H, N.
(()-r-1H-Imidazol-2-yl-r-(1-methyl-1H-pyrrol-3-yl)-1-
benzyl-4-piperidinemethanol (19). A mixture of diisopro-
pylamine (34 g, 0.337 mol) in tetrahydrofuran (1000 mL) was
stirred at -78 °C. Butyllithium (2.5 M) in hexane (126 mL,
0.314 mol) was added portionwise at -70 to -50 °C. The
mixture was stirred for 15 min at -50 to -78 °C. After
dropwise addition of a solution of 1-bis(ethoxy)methyl imida-
zole (55 g, 0.323 mol) in tetrahydrofuran at -70 °C, the
reaction mixture was further stirred for 1 h at -70 °C. A
solution of 18 (83.1 g, 0.294 mol) in tetrahydrofuran was added
dropwise at -70 °C. The reaction mixture was stirred for
another hour at -78 °C. The reaction mixture was allowed to
reach room temperature and was further stirred overnight at
room temperature. After quenching with water, acetic acid
(200 mL) was added dropwise over 15 min with the temper-
ature rising spontaneously to 35 °C. The reaction mixture was
stirred for 15 min at this temperature. The layers were
separated. The organic layer was further extracted with
diluted acetic acid. The combined acidic aqueous layers were
alkalized with potassium carbonate and extracted with dichlo-
romethane. This organic layer was dried on magnesium sulfate
and filtered, and the solvent was evaporated to afford quan-
titatively 103 g of 19 that was used in the next step without
further purification.
4-[1H-Imidazol-2-yl(1-methyl-1H-pyrrol-3-yl)methylene]-
1-benzylpiperidine (20a). A mixture of 19 (103 g, 0.294 mol)
in trifluoroacetic acid (1200 mL) was stirred and refluxed for
1 h. After evaporation of the solvent, the residue was poured
out into ice/water/potassium carbonate. This mixture was
extracted with dichloromethane. The organic layer was dried
on magnesium sulfate and filtered, and the solvent was
evaporated. Column chromatography over silica gel (eluent:
dichloromethane/methanol 95/5) followed by recrystallization
from acetonitrile afforded 74.0 g of 20a (75%). Mp: 188.2 °C.
Anal. (C21H24N4): C, H, N.
5,6-Dihydro-1′-benzylspiro[11H-imidazo[2,1-b][3]benz-
azepine-11,4′-piperidine] (25a). A mixture of 24 (270 g, 0.75
mol) in trifluoromethanesulfonic acid (1500 mL) was stirred
at 65 °C for 5 days and then cooled, poured out on ice, alkalized
with a sodium hydroxide 50% solution, and extracted with
dichloromethane. The organic layer was separated, dried on
magnesium sulfate, and filtered, and the solvent was evapo-
rated. Crystallization of the residue from diisopropyl ether/
acetonitrile (99/1) (1200 mL) afforded 169.6 g of 25a (66%).
Mp: 109.9 °C. Anal. (C23H25N3): C, H, N.
Methyl 2-[(1-Methyl-1H-pyrrol-3-yl)[1-benzyl-4-piper-
idinylidene]methyl]-1H-imidazole-1-acetate (20b). So-
dium hydride 50% (15.8 g, 0.33 mol) was added portionwise
to dimethylformamide at room temperature. 20a (74 g, 0.22
mol) dissolved in dimethyl formamide was then added drop-
wise and the mixture was stirred at room temperature for 1
h. Methyl chloroacetate (36.2 g, 0.33 mol) dissolved in di-
methylformamide was added dropwise and the mixture was
stirred at room temperature for 1 h. The mixture was poured
5,6-Dihydrospiro[imidazo[1,2-b][3]benzazepine-11-
[11H],4′-piperidine] (25b). A mixture of 25a (6.9 g, 0.02 mol)

Potent, Selective, Nonsedative H1 Antihistamines
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 6 2163
in methanol (150 mL) was hydrogenated with Pd/C 10% (2 g)
as a catalyst at 50 °C for 18 h. After uptake of hydrogen (1
equiv), the catalyst was filtered and the filtrate was evapo-
rated. Recrystallization of the residue as its hydrochloride salt
(1:1) in acetonitrile afforded 5 g of the hydrochloride salt of
25b (86%). Mp: 278.5 °C (HCl salt). Anal. (C16H19N3·HCl): C,
H, N.
tert-Butyl 5,6-Dihydrospiro[11H-imidazo[2,1-b][3]benz-
azepine-11,4′-piperidine]-1′-carboxylate (25c). Di-tert-
butyl dicarbonate (20.7 g, 0.095 mol) dissolved in a small
amount of dichloromethane was added dropwise to a stirring
mixture of 25b (free base) (20 g, 0.079 mol) in dichloromethane
(250 mL). The mixture was stirred at room temperature for
48 h and then washed with water, dried, and filtered, and the
solvent was evaporated. The residue was dissolved in diiso-
propyl ether and filtered. After evaporation of the filtrate,
column chromatography over silica gel (eluent: dichlo-
romethane/methanol 100/0 to 96/4) afforded 15.05 g of 25c
(54%). Mp: 107.4 °C. Anal. (C21H27N3O2): C, H, N.
tert-Butyl 3-Hydroxymethyl-5,6-dihydrospiro[11H-im-
idazo[2,1-b][3]benzazepine-11,4′-piperidine]-1′-carboxy-
late (26a) and tert-Butyl 2,3-Bis(hydroxymethyl)-5,6-
dihydrospiro[11H-imidazo[2,1-b][3]benzazepine-11,4′-
piperidine]-1′-carboxylate (27). A mixture of 25c (163 g,
0.46 mol), 37% formaldehyde in water (760 mL, 10.1 mol), and
sodium acetate (113 g, 1.38 mol) in acetic acid (68 mL) was
stirred and refluxed for 4 h. The mixture was cooled, poured
out on ice, alkalized with a sodium hydroxide 50% solution,
and extracted with dichloromethane. The organic layer was
separated, dried on magnesium sulfate, and filtered, and the
solvent was evaporated. Column chromatography over silica
gel (eluent: dichloromethane/methanol 97/3) afforded two pure
fractions that were recrystallized from acetonitrile, yielding
80.7 g of 26a [Yield: 46%. Mp: 200.0 °C. Anal. (C22H29N3O3):
C, H, N.] and 35 g of 27 [Yield: 18%. Anal. (C23H31N3O4): C,
H, N.].
tert-Butyl 3-Formyl-5,6-dihydrospiro[imidazo[2,1-b]-
[3]benzazepine-11,4′-piperidine]-1′-carboxylate (26b). A
mixture of 26a (59.5 g, 0.155 mol) and activated manganese
dioxide (300 g, 3.45 mol) in chloroform (1200 mL) was stirred
and refluxed for 90 min. The warm mixture was filtered over
dicalite and the filtrate was evaporated. Recrystallization of
the residue from acetonitrile afforded 51.8 g of 26b (88%).
Mp: 156.5 °C. Anal. (C22H27N3O3): C, H, N.
Methyl tert-Butyl 5,6-dihydrospiro[11H-imidazo[2,1-
b][3]benzazepine-11,4′-piperidine]-3,1′-dicarboxylate (26c).
A mixture of 26b (51.2 g, 0.134 mol), sodium cyanide (34.6 g,
0.705 mol), and activated manganese dioxide (233 g, 2.68 mol)
in methanol (2500 mL) was stirred at room temperature. Acetic
acid (45.5 mL) was added dropwise. The mixture was stirred
and refluxed for 20 h and filtered over dicalite. The filtrate
was evaporated and the residue was taken up in water,
dichloromethane, and potassium carbonate. After separation,
the aqueous layer was extracted with dichloromethane. The
combined organic layers were dried on magnesium sulfate and
filtered, and the solvent was evaporated. Column chromatog-
raphy over silica gel (eluent: dichloromethane/ methanol 97/
3) afforded 47.7 g of 26c (87%) that was used in the next step
without further purification.
1′-[tert-Butoxycarbonyl]-5,6-dihydrospiro[11H-imidazo-
[2,1-b][3]benzazepine-11,4′-piperidine]-3-carboxylic Acid
(26d). A mixture of 26c (23 g, 0.056 mol) in 1 N sodium
hydroxide (100 mL), water (250 mL), and tetrahydrofuran (250
mL) was stirred at room temperature for 18 h. The organic
solvent was evaporated. The aqueous concentrate was neutral-
ized with 1 N hydrochloric acid (100 mL) and extracted with
dichloromethane. The organic layer was dried on magnesium
sulfate and filtered, and the solvent was evaporated to afford
22.9 g of 26d (100%) after recrystallization in acetonitrile.
Anal. Calcd for C22H27N3O4: C, 66.48; H, 6.85; N, 10.57.
Found: C, 65.42; H, 6.74; N, 10.74.
thylaminopyridine (4.9 g, 0.04 mol) in dichloromethane (300
mL) was stirred until complete dissolution. Triethylamine (5.6
g, 0.05 mol) was added followed by EDCI (9.6 g, 0.05 mol).
After stirring for 30 min at room temperature, triethylamine
(5.6 g, 0.06 mol) was added followed by ammonium chloride
(2.7 g, 0.05 mol). The mixture was stirred at room temperature
overnight, poured out into water, and separated. The aqueous
layer was extracted with dichloromethane. The combined
organic layer was dried on magnesium sulfate and filtered,
and the solvent was evaporated. Column chromatography over
silica gel (eluent: dichloromethane/methanol 97.5/2.5) followed
by crystallization from acetonitrile afforded 9.5 g of 26e (60%).
Anal. (C22H28N4O3): C, H, N.
5,6-Dihydrospiro[11H-imidazo[2,1-b][3]benzazepine-
11,4′-piperidine]-3-carboxamide Dihydrochloride (3a). A
mixture of 26e (9 g, 0.023 mol) in 6 N hydrochloric acid in
2-propanol (25 mL) and methanol (100 mL) was stirred and
refluxed for 90 min. After cooling, the precipitate was filtered
and dried to afford 8 g of 3a (94%). Mp: >250 °C (dec). 1H
NMR (400 MHz, DMSO-d6): δ 2.57 (ddd, J ) 14.7, 10.7, 4.3
Hz, 2 H), 3.02 (br.d, J ) 14.6 Hz, 2 H), 3.21 (m, 4 H), 3.43 (t,
J ) 7.0 Hz, 2 H), 4.98 (t, J ) 7.0 Hz, 2 H), 7.27 (m, 3 H), 7.46
(m, 1 H), 7.57 (br.s, 1 H), 7.93 (s, 1 H), 8.03 (br.s, 1 H), 9.29
(br.m, 2 H); 13C NMR (101 MHz, DMSO-d6) δ 31.2, 31.5, 40.7,
41.8, 43.2, 125.3, 127.0, 127.1, 127.9, 132.5, 136.6, 138.7, 150.1,
160.5. Anal. (C17H20N4O·2HCl): C, H, N.
3-Bromo-5,6-dihydro-1′-benzylspiro[11H-imidazo[2,1-
b][3]benzazepine-11,4′-piperidine (28a). N-Bromosuccin-
imide (16 g, 0.09 mol) was added portionwise over 1 h to a
solution of 25a (31 g, 0.09 mol) in dichloromethane (1000 mL)
cooled to 0 °C. Water was then added and the organic layer
was separated, washed with water, dried, and filtered, and
the solvent was evaporated. Column chromatography over
silica gel (eluent: dichloromethane/methanol 97.5/2.5 to 95/
5) afforded 10.9 g (35%) of starting material 25a and 28a that
was converted to its fumarate salt (1:1) in ethanol, yielding
17.3 g (36%) of this salt. Mp: 218.0 °C. Anal. (C23H24BrN3·
C4H4O4): C, H, N.
5,6-Dihydro-1′-benzylspiro[11H-imidazo[2,1-b][3]ben-
zazepine-11,4′-piperidine]-3-carboxamide (28b). A mix-
ture of 28a (12.9 g, 0.03 mol), palladium(II) acetate (0.135 g,
0.0006 mol), and 1,3-bis(diphenylphosphino)propane (0.495 g,
0.0012 mol) in tetrahydrofuran (200 mL) was stirred in an
autoclave at 150 °C for 16 h under pressure of carbon monoxide
(30 atm) and ammonia (10 atm). The mixture was filtered and
the filtrate was evaporated. Column chromatography on silica
gel (eluent: dichloromethane/methanol 95/5 to 90/10) afforded
8.3 g of 28b (72%). For analytical purposes, a sample of 28b
was converted into its fumarate salt (1:1) in ethanol. Anal.
Calcd for C24H26N4O·C4H4O4·H2O.0.4C2H6O: C, 64.16; H, 6.44;
N, 10.39. Found: C, 63.74; H, 6.35; N, 10.59.
5,6-Dihydrospiro[11H-imidazo[2,1-b][3]benzazepine-
11,4′-piperidine]-3-carboxamide (3b). A mixture of 28b (36
g, 0.093 mol) in methanol (250 mL) was hydrogenated for 32
h at 50 °C in the presence of Pd/C 10% (2 g). After uptake of
hydrogen (1 equiv), the catalyst was filtered off and the filtrate
was evaporated. The solid residue was triturated in diisopropyl
ether, filtered, and dried at 40 °C under vacuum for 16 h,
yielding 23 g (83%) of the free base 3b. Mp: 249.0 °C.
1H NMR of this compound confirmed that it was identical
to a sample prepared by liberating the base from the dihy-
drochloride 3a prepared according to the above procedure.
Determination of the Aqueous Solubility of 3a and 3b
as a Function of the pH. Solubility was studied according
to the method of Higuchi and Connors.27 The solutes 3a or 3b
(an excess or the amounts indicated in Table 2) were added to
25 mL glass vials containing the solvent. The closed vials were
shaken for 24 h at 20 °C. If the mixture were clear solutions,
the pH was recorded and no further analysis was performed.
The results, reported for the clear mixtures, are based on the
ratio of added solute over the volume of solvent used. For the
turbid samples, the excess was removed by filtration over a
0.45 µm membrane filter (Millipore), the pH of the filtrates
tert-Butyl 3-(Aminocarbonyl)-5,6-dihydrospiro[11H-
imidazo[2,1-b][3]benzazepine-11,4′-piperidine]-1′-carbox-
ylate (26e). A mixture of 26d (15.9 g, 0.04 mol) and 4-dime-

2164 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 6
Janssens et al.
were recorded, and the concentration of 3a or 3b in solution
48/80. Criterion for drug-induced protection: >240 min sur-
vival (in historical controls: 5.0%; n > 1000).
was determined using UV absorption analysis.
Receptor Binding Affinity for the Human Cloned
Histamine H1 Receptor Expressed in CHO Cells.28 The
radioligand used was [3H]pyrilamine (1 nM, New England
Nuclear NET-594). The blank was astemizole (1 µM). The
tissue used was cloned human histamine-H1 CHO-K1 cells. A
Na+, K+ phosphate buffer (50 mM, pH 7.5) was used (a 50 mM
solution of K2HPO4 was adjusted to pH 7.5 with 50 mM NaH2-
PO4).
Histamine-Induced Lethality in Guinea Pigs.20a
His-
tamine (1.25 mg/mL/kg, iv)-induced lethality was recorded in
guinea pigs of both sexes (300-500 g) up to 120 min after the
histamine challenge. Test compound or solvent was adminis-
tered at specified time intervals before histamine. Criterion
for drug-induced protection: >120 min survival (0.0% false
positives controls; n > 150). Histamine H1 antagonists protect
against the histamine-induced lethality.
Skin Reaction Test in Rats (modification of ref 21).
Fifty hours after passive sensitization of a dorsal skin site by
intradermal injection (0.05 mL) of ovalbumin-specific IgE-
containing serum, three additional dorsal skin sites were
injected intradermally with histamine (50 µg), serotonin (0.1
µg), and Ascaris allergens (1/2 diluted with saline) in male rats
(200-240 g). Immediately thereafter, the animals were chal-
lenged iv with a mixture (1 mL) of ovalbumin (1%) and Evans
blue dye (0.2%) and sacrificed 30 min later. The intensity of
the blue-colored skin reactions was scored by two independent
observers in comparison with standard reactions. The scoring
system was (4) maximal, (3) pronounced, (2) moderate, (1)
slight, and (0) no difference with surrounding skin. The scores
of the two observers were summed for further evaluation. Test
compound or solvent was administered 2 h before induction
of the skin reactions. Criteria for drug-induced effects are as
follows: (A) serotonin reactions, score < 4 for inhibition and
score < 3 for blockade (occurring in 2.1% and 1.2%, respec-
tively, of solvent-treated control rats; n ) 521); (B) histamine
reactions, score < 4 for inhibition and score < 3 for blockade
(occurring in 5.6% and 2.9%, respectively, of the control rats);
(C) PCA reactions: score < 3 for inhibition (occurring in 6.3%
of the control rats); and (D) Ascaris allergens reactions: score
< 3 for inhibition (occurring in 3.6% of the control rats).
Skin Reaction Test in Guinea Pigs. Five dorsal skin sites
of guinea pigs of both sexes (300-500 g) were injected
intradermally (0.05 mL) with saline containing substance P
(0.05 µg), histamine (0.25 µg), bradykinin (0.1 µg), PAF
(0.00625 µg), and Ascaris allergens (1/16 diluted with saline).
Immediately thereafter, the animals were challenged i.v. with
Evans blue dye (30 mg/kg: 7.5 mg/mL, 4 mL/kg) and sacrificed
30 min later. The intensity of the blue-colored skin reactions
was scored by two independent observers in comparison with
standard reactions. The scoring system was: (4) maximal, (3)
pronounced, (2) moderate, (1) slight, and (0) no difference with
surrounding skin. The scores of the two observers were
summed for further evaluation. Test compound or solvent was
administered at a predefined interval before induction of the
skin reactions. Criteria for drug-induced effects: (1) histamine
reactions: score < 7 for inhibition and score < 3 for blockade
(occurring in 3.6% and 0.0%, respectively, of solvent-treated
control guinea-pigs; n ) 56); (2) substance P reactions: score
< 7 for inhibition, score < 5 for pronounced inhibition, and
score < 3 for blockade (occurring in 3.6%, 0.0% and 0.0%,
respectively, of controls); (3) PAF reactions: score < 7 for
inhibition and score < 3 for blockade (occurring in 0.0% and
0.0%, respectively, of controls); (4) bradykinin reactions: score
< 7 for inhibition and score < 3 for blockade (occurring in 0.0%
and 0.0%, respectively, of controls); and, (5) Ascaris allergens
reactions: score < 3 for blockade (occurring in 5.4% of
controls).
CHO-cells expressing the cloned human H1 receptor were
cultured in HAM’S F12 medium (GIBCO cat. no. 21765-029)
enriched with 10% HI fetal calf serum and in the presence of
penicillin (105 IU/L) and streptomycin sulfate (100 mg/L).
Twenty-four hours before collection, cells were induced with
5 mM sodium butyrate and prepared on the day of confluence
(70-90%). On the day of experiment, cell membranes, stored
at -70 °C, were thawed and homogenized in homogenization
buffer using an Ultra Turrax homogenizer in an appropriate
dilution, based on the results of an initial dilution experiment.
Incubation was carried out for 30 min at 25 °C. Reactants were
pipetted in plastic 5-mL tubes, 3 mL of ice-cold rinsing buffer
was added to the tubes followed by rapid filtration over GF/B
filters, and filters were rinsed twice with ice-cold rinsing buffer
and placed into counting vials. LKB Ultima Gold (5 mL) was
added, and counting was carried out in a Packard liquid
scintillation counter. Results were expressed in dpm. The
compounds were investigated for interaction with [3H]pyril-
amine binding at different concentrations.
Animals for the Pharmacological Tests. Wistar rats,
Dunkin-Hartley-Purbright guinea pigs, and internally bred
Beagle dogs were used. Unless otherwise stated, they were
transferred to the air-conditioned laboratories on the day
before the experiment and housed in individual cages under
standard laboratory conditions (21 ( 2 °C; 65 ( 15% relative
humidity; light-dark cycle set at 12 h). They were food-deprived
overnight but tap water remained available ad libitum except
during the test period.
Test Compounds. Compounds 1, 2a, 3a and cetirizine (5)
were prepared as solutions in distilled water, and loratadine
(4) was dissolved in 10% hydroxypropyl-â-cyclodextrin contain-
ing 1 equiv of tartaric acid. The concentrations were selected
to obtain the desired doses using a standard administration
volume of 10 mL/kg. The solutions were stored at room
temperature in closed containers protected from light. They
were studied at a predefined interval after single subcutaneous
(sc) or oral (po) administration. All doses were expressed in
mg of base equivalents per kg of body weight.
General Procedure and Statistics for the in Vivo
Models for Evaluation of Antihistaminic Activity in
Rats, Guinea Pigs, and Dogs. All experiments were per-
formed by unbiased trained technicians using coded solutions.
Doses were selected from the geometrical series 0.04, 0.08,
0.16, 0.32, 0.63, 1.25, 2.5, 5.0, 10 mg/kg in such a way that at
least three doses covered the dose-response curve. Each dose
group in this most relevant part of the dose-response curve
consisted of five animals that were tested in separate daily
experimental sessions in order to account for day-to-day
variability and to minimize systematic errors. Control injec-
tions of solvent were included in each experimental session.
All-or-nothing criteria for significant (p < 0.05) effects were
defined by analyzing a frequency distribution of a large series
of historical control data. ED50 values and corresponding 95%
confidence limits were calculated according to the method of
Finney for categorical data.29
Ascaris Allergens-Induced Skin Reaction Test in Dogs
(modification of ref 22). A preparation of Ascaris allergens
(ACF; 1/100 diluted with saline; 0.05 mL) was injected at three
skin sites close to the chest in dogs of both sexes, varying in
body weight, and selected for sensitivity to Ascaris allergens.
Fifteen minutes later, the wheal diameters (φ, in mm) and skin
thickness increases (TI; the difference in 0.1 mm between the
center of the reaction and the mean of two surrounding normal
skin sites) were measured. After these 0-h time values, test
compound or solvent was administered orally to the dogs. The
three injections of ACF and the measurements were repeated
1, 4, 20, and 72 h after the oral administration of the test
compounds. The test compounds were tested at several dose
Compound 48/80-Induced Lethality in Rats.19 Injection
of compound 48/80 in rats results in a massive release of mast-
cell mediators, which are in rats predominantly histamine and
serotonin. The resulting lethal anaphylactic shock is counter-
acted by histamine H1 antagonists. The compound 48/80 (0.50
mg/kg, iv)-induced lethality was recorded in female rats (225-
275 g) up to 240 min after injection. Test compound or solvent
was administered at specified time intervals before compound

Potent, Selective, Nonsedative H1 Antihistamines
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 6 2165
(3) McTavish, D.; Goa, K. L.; Ferrill, M. Terfenadine: An updated
review of its pharmacological properties and therapeutic efficacy.
Drugs 1990, 39 (4), 552-574.
(4) Curran, M. P.; Scott, L. J.; Perry, C. M. Cetirizine. A Review of
its Use in Allergic Disorders. Drugs, 2004, 64 (5), 523-561.
(5) Haria, M.; Fitton, A.; Peters D. H. Loratadine. A Reappraisal of
its Pharmacological Properties and Therapeutic Use in Allergic
Disorders. Drugs, 1994, 48 (4), 617-637.
(6) (a) Simons, F. E. R.; Kesselman, M. S.; Giddins, N. G.; Pelech,
A. N.; Simons, K. J. Astemizole induced torsade de pointes.
Lancet 1988; II (8611), 624. (b) Davies, A. J.; Harindra, V.;
McEwan, A.; Ghose, R. R. Cardiotoxic effect with convulsions
in terfenadine overdose. Br. Med. J. 1989 298 (6669), 325. (c)
Wiley, J. F.; Gelber, M. L.; Henretig, F. M.; Wiley, C. C.; Sandhu,
S.; Loiselle, J. Cardiotoxic effects of astemizole overdose in
children. J. Pediatr. 1992 120 (5), 799-802. (d) Woolsey, R. L.;
Chen, Y.; Freiman J. P.; Gillis, R. A. Mechanisms of the
cardiotoxic actions of terfenadine. JAMA 1993, 269 (12), 1532-
1536. (e) Woolsey, R. L. Cardiac actions of antihistamines. Annu.
Rev. Pharmacol. Toxicol. 1996; 36, 233-252. (f) Salata, J. J.;
Jurkiewicz, N. K.; Wallace, A. A.; Stupienski, R. F.; Guinosso,
P. J.; Lynch, J. J. Cardiac electrophysiological actions of the
histamine H1-receptor antagonists astemizole and terfenadine
compared with chlopheniramine and pyrilamine. Circ. Res. 1995;
76 (1), 110-119. (g) Rampe, D.; Wible, B.; Brown, A. M.; Dage,
R. C. Effects of terfenadine and its metabolite on a delayed
rectifier K+ channel from human heart. Mol. Pharmacol. 1993,
44 (6), 1240-1245.
levels in separate sessions. The results are expressed as wheal
volumes (in mm3) obtained by the formula
2
φ
TI
20
π
( ) (
)
2
On the basis of frequency distributions of the volumes mea-
sured at the four time intervals in control animals (n > 600),
the following all-or-nothing criteria were selected for deter-
mining ED50 values: <115 mm3 for the 1-, 4-, 20-, and 72-h
intervals (occurrence in 1.5%, 1.2%, 4.1%, and 1.0% in control
dogs; n ) 882).
Determination of H1 Receptor Occupancy in Guinea
Pig Brain. In vivo H1 receptor occupancy in guinea pig brain
was measured by ex vivo autoradiography according to our
standard protocol.23 Male Dunkin-Hartley guinea pigs (300
g) were treated by oral administration of vehicle or tested
compounds at seven dosages ranging from 0.01 to 40 mg/kg of
body weight (dosages: 0.01, 0.04, 0.16, 0.63, 2.5, 10, and 40
mg/kg, n ) 3-9 animals per dose) and sacrificed 3 h later.
The brains were immediately removed from the skull and
rapidly frozen in dry-ice-cooled 2-methylbutane (-40 °C).
Twenty-micrometer-thick sections were cut using a Leica CM
3050 cryostat-microtome and thaw-mounted on microscope
slides. The sections were then kept at -20 °C until use.
Occupancy of H1 receptors was measured in the cerebellum of
each individual guinea pig. After thawing, the sections were
dried under a stream of cold air and then incubated for 10
min in 50 mM Na/K phosphate buffer (pH 7.4) containing 4
nM [3H]pyrilamine. Nonspecific binding was measured on
adjacent sections in the presence of 1 µM astemizole. After
the incubations, the slides were washed (2 × 2 min) in ice-
cold buffer, followed by a quick rinse in ice-cold water. The
sections were then dried under a stream of cold air and exposed
(7) Geha, R. S.; Meltzer, E. O. Desloratadine: A New, Nonsedating,
Oral Antihistamine. J. Allergy Clin. Immunol. 2001, 107 (4),
751-762.
(8) Casale, T. B.; Blaiss, M. S.; Gelfand, E.; Gilmore, T.; Harvey, P.
D.; Hindmarch, I.; Simons, F. E.; Spangler, D. L.; Szefler, S. J.;
Terndrup, T. E.; Waldman, S. A.; Weiler, J.; Wong, D. F.
Antihistamine Impairment Roundtable. First do no harm: Man-
aging antihistamine impairment in patients with allergic rhini-
tis. J. Allergy Clin. Immunol. 2003, 111 (5), S835-S842.
(9) Stanaland, B. E. Treatment of Patients with Chronic Idiopathic
Urticaria. Clin. Rev. Allergy Immunol. 2002, 23 (2), 233-241.
(10) Janssens, F.; Leenaerts, J.; Van Roosbroeck, Y.; Sommen, C.;
De Boeck, B. A Simple and General Synthesis of 4-(Spiro-
[imidazobenzazepine])-piperidine and its Analogues. Manuscript
in preparation.
(11) Bold, G.; Capraro, H.-G.; Faessler, A.; Lang, M.; Bhagwat, S.
S.; Khanna, S. C.; Lazdins, J. K.; Mestan, J. Preparation of
ethers of aspartate protease substrate isosteres as antivirals.
Eur. Pat. Appl. 1996, EP708085.
(12) Janssens, F. E.; Diels, G. S. M.; Leenaerts, J. E.; Cooymans, L.
P. Preparation of imidazo[1,2-a](pyrrolo, thieno or furano)[3,2-
d]azepines as allergy inhibitors. Eur. Pat. Appl. 1992, EP518434.
(13) Donetti, A.; Boniardi, O.; Ezhaya, A.; Phase-Transfer Catalyzed
Oxidative Decyanation of R-Secondary Nitriles; A Convenient
Synthesis of Aromatic Ketones. Synthesis 1980, (12), 1009-1011.
(14) Carson, J. R.; Davis, N. M.; Acid-mediated rearrangement of
acylpyrroles. J. Org. Chem. 1981, 46 (5), 839-843.
(15) ter Laak, A. M.; Bijloo, G. J.; Fischer, M. J. E.; Donne´ op den
Kelder, G. M.; Wilting, J.; Timmerman, H. Serum protein
binding of histamine H1-antagonists. A comparative study on
the serum protein binding of a sedating ([3H]mepyramine) and
a nonsedating H1-antagonist ([3H]loratadine). Eur. J. Pharm.
Sci. 1996, 4 (5), 307-319.
(16) Kasim, N. A.; Whitehouse, M.; Ramachandran, C.; Bermejo, M.;
Lennerna¨s, H.; Hussain, A. S.; Junginger, H. E.; Stavchansky,
S. A.; Midha, K. K.; Shah, V. P.; Amidon, G. L. Molecular
Properties of WHO Essential Drugs and Provisional Biophar-
maceutical Classification. Mol. Pharm. 2004, 1 (1), 85-96.
(17) Pagliara, A.; Testa, B.; Carrupt, P.-A.; Jolliet, P.; Morin, C.;
Morin, D.; Urien, S.; Tillement, J.-P.; Rihoux, J.-P. Molecular
Properties and Pharmacokinetic Behavior of Cetirizine, a Zwit-
terionic H1-Receptor Antagonist. J. Med. Chem. 1998, 41 (6),
853-863.
(18) Briejer, M. R.; Bosmans, J.-P.; Van Daele, P.; Jurzak, M.; Heylen,
L.; Leysen, J. E.; Prins, N. H.; Schuurkes, J. A. J. The in vitro
pharmacological profile of prucalopride, a novel enterokinetic
compound. Eur. J. Pharmacol. 2001, 423 (1), 71-83.
(19) Niemegeers, C. J. E.; Awouters, F.; Van Nueten, J. M.; De Nollin,
S.; Janssen, P. A. J. Protection of Rats from Compound 48/80-
induced Lethality. A Simple Test for Inhibitors of Mast Cell-
mediated Shock. Arch. Int. Pharmocodyn. Ther. 1978, 234 (1),
164-176.
3
to H-Hyperfilms (Amersham, U.K.) for 4 weeks. Autoradio-
grams were quantified using a MCID image analyzer (Imaging
Research, St-Catharines, Ontario, Canada). Specific binding
was given as the difference between total binding and non-
specific binding measured in adjacent sections. Percentages
of H1 receptor occupancy by the drug administered to the
animal correspond to 100% minus the percentage of H1
receptor labeling in the treated animal. The percentage of H1
receptor occupancy was plotted against dosage and the sig-
moidal log dose-effect curve of best fit was calculated by
nonlinear regression analysis, using the GraphPad Prism
program. From these dose-response curves, the ED50s (the
drug dose producing 50% receptor occupancy) were calculated.
Acknowledgment. TheauthorsthankJanD’Aubioul,
Alex De Groot, An Hermans, Jef Peeters, Ard Teisman,
and Jef Vermeire for their help.
Supporting Information Available: Table of detailed
1
elemental analysis results, H NMR data for the intermedi-
ates, and 13C NMR data for selected intermediates. This
material is available free of charge via the Internet at http://
pubs.acs.org.
References
(1) For a selection of representative reviews on antihistamines,
see: (a) Sneader, W. Histamine and the Classic Antihistamines.
Drug News Perspect. 2001, 14 (10), 618-624. (b) Walsh, G. M.;
Annunziato, L.; Frossard, N.; Knol, K.; Levander, S.; Nicolas,
J.-M.; Taglialatela, M.; Tharp, M. D.; Tillement, J. P.; Timmer-
man, H. New Insights into the Second Generation Antihista-
mines. Drugs 2001, 61 (2), 207-236. (c) Oppenheimer, J. J.;
Casale, T. B. Next Generation Antihistamines: Therapeutic
Rationale, Accomplishments and Advances. Expert Opin. Inves-
tig. Drugs 2002, 11 (6), 807-817. (d) Hindmarch, I. CNS Effects
of Antihistamines: Is There a Third Generation of Nonsedative
Drugs? Clin. Exp. All. Rev. 2002, 2, 26-31. (e) Rihoux, J. P. H1-
Receptor Antagonists: A Critical Reapparaisal. IDrugs 1999, 2
(12), 1295-1301.
(20) (a) Van Wauwe, J.; Awouters, F.; Niemegeers, C. J. E.; Janssens,
F.; Van Nueten, J. M.; Janssen, P. A. J. In vivo Pharmacology
of Astemizole, a new type of H1-antihistaminic Compound. Arch.
Int. Pharmocodyn. Ther. 1981, 251 (1), 39-51. (b) Awouters, F.;
Niemegeers, C. J. E.; Janssen, P. A. J. Inhibitors of Mast Cell-
(2) Janssens, F.; Torremans, J.; Janssen, M.; Stokbroekx, R. A.;
Luyckx, M.; Janssen, P. A. J. New Antihistaminic N-Heterocyclic
4-Piperidinamines. 2. Synthesis and Antihistaminic Activity of
1-[(4-Fluorophenyl)methyl]-N-(4-piperidinyl)-1H-benzimidazol-
2-amines . J. Med. Chem. 1985, 28 (12), 1934-1943.

2166 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 6
Janssens et al.
mediated shock in the Rat: Relationship to Histamine and
Serotonin Antagonism. Drug Dev. Res. 1981, 1 (2), 107-114.
(21) Awouters, F.; Niemegeers, C. J. E.; Janssen, P. A. J. Interaction
of astemizole and other drugs with Passive Cutaeous Anaphy-
lactic and histamine, serotonin, and compound 48/80-induced
skin reactions in the rat. A procedure to determine anti-allergic
effectiveness. Drug Dev. Res. 1985, 5 (2), 137-145.
(22) Awouters, F.; Vermeire, J.; Smeyers, F.; Vermote, P.; Van Beek,
R.; Niemegeers, C. J. E. Oral antiallergic activity in Ascaris
hypersensitive dogs: A study of known antihistamines and of
the new compounds ramastine (R57959) and levocabastine
(R50547). Drug Dev. Res. 1986, 8 (1-4), 95-102.
(25) De Ponti, F.; Poluzzi, E.; Cavalli, A.; Recanatini, M.; Montanaro,
N. Safety of nonantiarrhythmic drugs that prolong the QT
interval or induce torsade de pointes: An overview. Drug Saf.
2002, 25 (4), 263-286.
(26) Zhou, Z.; Vorperian, V. R.; Gong, Q.; Zhang, S.; January, C. T.
Block of HERG potassium channels by the antihistamine
astemizole and its metabolites desmethylastemizole and no-
rastemizole.
843.
J Cardiovasc. Electrophysiol. 1999, 10, 836-
(27) Higuchi, T.; Connors, K. A. In Advances in Analytical Chemistry
and Instrumentation; Reilly, C. N., Ed.; Wiley-Interscience: New
York, 1995; Vol. 4, p 117.
(23) Schotte, A.; Janssen, P. F. M.; Gommeren, W.; Luyten, W. H.
M. L.; Van Gompel, P.; Lesage, A. S.; De Loore, K.; Leysen, J.
E. Risperidone compared with new and reference antipsychotic
drugs: In vitro and in vivo receptor binding. Psychopharmacol-
ogy 1996, 124 (1/2), 57-73.
(24) Ahnaou, A.; Megens, A. A. H. P.; Drinkenburg, W. H. I. M. The
atypical antipsychotics risperidone, clozapine and olanzapine
differ regarding their sedative potency in rats. Neuropsychobi-
ology 2003, 48 (1), 47-54.
(28) De Backer, M. D.; Gommeren, W.; Moereels, H.; Nobels, G.; Van
Gompel, P.; Leysen, J. E.; Luyten, W. H. M. L. Genomic cloning,
heterologous expression and pharmacological characterisation
of a human histamine H1 receptor. Biochem. Biophys. Res.
Commun. 1993, 197, 1601-1608.
(29) Finney, D. J. Probit analysis; Cambridge University Press:
Cambridge, 1962.
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